Test clip contact arrangement

ABSTRACT

A connecting device is described for use in a test clip whose multiple contacts engage multiple leads of an IC (integrated circuit) device, which can be constructed reliably and at low cost. The test clip includes a flat flexible cable (54, FIG. 7 ) mounted on a clip housing, the cable having parallel conductors (50) mounted on insulation 53. Lower end portions of the conductors serve as lead-engaging contacts. Each conductor lower end portion extends in a substantially 180° loop (62), with one side (70) of each loop being positioned to engage a corresponding lead of the IC device.

CROSS REFERENCE TO RELATED APPLICATION:

This is a continuation-in-part of patent application Ser. No. 893,181filed June 3, 1992, now abandoned.

BACKGROUND OF THE INVENTION:

Test clips are used to temporarily connect to the leads of IC(integrated circuit) devices. High density circuits generally have arectangular body and multiple leads extending from two or four sides ofthe body to a circuit board. Present test clips use rows of individualcontacts, each stamped or photo-fabricated to small tolerances. Thecontacts are placed in individual slots of a plastic housing, and areseparated by thin barriers that form the slots.

IC devices are becoming available with greater numbers of leads spacedcloser together. IC devices are currently available with fifty leads oneach of four sides, having a 0.5 mm (0.02 inch) lead pitch, which is thecenter-to-center spacing of the leads. It is expected that IC deviceswill soon be available with lead pitch sizes of 0.4 mm and 0.3 mm. Asthe pitch size decreases, the size and tolerance of the very thincontacts and of the insulator barrier walls between adjacent contacts,becomes extremely small. The problem of producing reliable test clipsfor such miniature IC devices is compounded by the fact that existing ICdevices as well as recently announced new ones are not wellstandardized. A connecting device which enabled test clips to bemanufactured at moderate cost to reliably engage the leads of IC deviceshaving leads spaced at very small pitch sizes, would be of considerablevalue in the testing of IC circuit devices.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a connectingdevice is provided which is especially useful in a test clip whichrequires multiple conductors with closely spaced contact ends that canreliably make wiping contact with leads or terminals. The connectingdevice includes a flat flexible cable having a group of elongatedconductors held in a fixed relationship by insulation. The conductorsextend parallel to each other and are laterally spaced apart, with eachconductor having a contact end for engaging a lead or terminal. Eachcontact end is formed by a portion of a conductor that extends in aloop. The loop configuration results in each contact end being curved,which avoids the presence of sharp edges in very small contact ends.

A test clip can use the flat flexible cable connecting device to engagethe largely vertical outer lead parts of a row of leads extending from aside of an IC device. The cable is oriented so the looped conductor endsproject downwardly and make wiping contact with the outer lead parts asthe test clip is pressed down onto the IC device.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified isometric view of a test clip constructed inaccordance with the present invention, and showing it lying above anintegrated circuit device that is mounted on a circuit board.

FIG. 2 is a side elevation view of the test clip of FIG. 1.

FIG. 3 is a plan view, partially in section, of the test clip of FIG. 2.

FIG. 4 is a sectional view of the test clip of FIG. 2.

FIG. 5 is a view of a portion of FIG. 4.

FIG. 6 is an enlarged view of a portion of the connector of FIG. 5, andshowing it engaged with an integrated circuit device.

FIG. 7 is a partial isometric sectional view of the connecting device ofthe test clip of FIG. 6.

FIG. 8 is a partial elevation view of the connecting device of FIG. 7.

FIG. 9 is a sectional side view of a flat flexible cable of theconnecting device of the invention, shown prior to forming of loops atthe contact ends thereof.

FIG. 10 is a plan view of the cable of FIG. 9.

FIG. 11 is a sectional side view of the flat flexible cable of FIG. 9,shown after bending to form loops at the contact ends thereof.

FIG. 12 is a bottom view of the cable of FIG. 11.

FIG. 12A is a view of a portion of the cable of FIG. 9.

FIG. 13 is a partial bottom view of the test clip of FIG. 2.

FIG. 14 is a partial isometric view of the test clip of FIG. 13.

FIG. 15 is a partial sectional view of a test clip constructed inaccordance with another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a test clip 10 of the present invention, which can belowered onto a surface mounted IC (integrated circuit) device 12. The ICdevice has been mounted on a circuit board device, or circuit board 14,of electronic equipment. The particular IC device is a CQFP (ceramicquad flat pack) IC device which includes 100 leads projectinghorizontally from a body 18. Twenty five leads project from each of foursides 21-24 of the body. The body has a top 26 that faces upwardly whenthe circuit board (its upper surface) lies in a horizontal plane, andhas a bottom 28 that lies adjacent to the upper face 29 of the circuitboard.

As shown in FIG. 4, the test clip includes a clip housing 30 withlocating walls 32, 34 that engage the body of an IC device to accuratelylocate the test clip with respect to the IC device. The clip has aplurality of lead-engaging contacts 36 which engage the leads of the ICdevice. The lead-engaging contacts 34 are electrically coupled tocontact elements 38 of a connector 40 of the header type. The test cliphousing includes a test clip board 42 of a test clip circuit boardassembly 44, and the connector 40 is mounted on the board 42.

As shown in FIG. 6, the lead-engaging contacts 36 which engage leads 16of the IC device 12, are formed by conductors 50 of a flat flexiblecable 52. The flat flexible cable serves as a connecting device with oneend that makes temporary engagement with terminals or leads such as theleads 16 of the IC device, and which has another end which connects toother leads or terminals such as the contact elements of the headerconnector 40 (FIG. 4). The cable 52 (FIG. 6) includes flexibleinsulation 53 which intimately surrounds at least portions of theconductors. As shown in FIG. 7, a group 54 of conductors which includesthe individual conductors 50, are held by the insulation 53 in a fixedrelationship wherein the conductors extend parallel to each other andare spaced from each other along a predetermined lateral direction L.The group of conductors has a first end portion forming the contact endsor contacts 36 of the conductors. Lower or first end portions 60 of theconductors are formed in substantially parallel conductor loops 62 thatare each curved about an axis 64 extending parallel to the lateraldirection.

As shown in FIG. 8, each loop includes first and second sides 70, 72joined by a middle 74. At least the first side 70 of the loop has anexposed outer surface 76. When the test clip 10 of FIG. 6 is installedon the IC device 12 by moving the test clip down, the first side 70 ofthe loop initially engages a lead 16 of the IC device. Each lead 16generally has a horizontal upper part 80 and has an outer lead part 82that extends largely vertically and ends in an outer part 84. When thetest clip 10 is moved downwardly towards the IC device, the partiallylowered loop at 62A initially engages the outer lead part 82 at aninitial contact point 90 (actually line contact may be made) on thefirst side 70 of the loop. When locating wall 32 engages the top 26 ofthe IC device body, the loop will have moved down to the position 62B,wherein it engages the outer lead part at a final contact point 92. Bothcontact points lie on the first side 70 of the loop middle 74. Duringengagement, the contact loop makes wiping contact with the lead, and thecontact loop is also wiped, which encourages low resistance engagement.

Applicant earlier used a flat flexible cable, with exposed lower endsforming a row of contacts, but with the lower ends merely cut. Thecutting of the conductor ends can leave burrs or other unevenness. Theextreme tip of cut conductors, can lead to the exposed conductor ends"catching" on the leads and not becoming gradually deflected to one sidebut instead becoming severely bent. Such bending can result in aconductor not engaging a lead of a next IC device to which the test clipis connected. Applicant's provision of a loop results in the lower endof each contact having a gradual curvature, which avoids sharp or burredtips that could catch on a lead or other part. The two sides of the loopsupport each other through the middle 74, which avoid twisting or otherunwanted deformation of the contacts.

FIGS. 9-12 show the manner in which the flat flexible cable connectordevice 52 is formed. FIGS. 9 and 10 show the cable at 52A, with theconductor 50 not yet bent. The cable includes first and secondinsulation layers 100, 102, which are interrupted at a gap 104. The gapresults in first and second insulation parts 106, 108, with each partincluding insulation surrounding each conductor 50. Applicant prefers toprovide a stiffening layer of insulation 110 at an upper end 112 of thecable.

FIGS. 11 and 12 show the cable at 52B after its lower end 114 has beenbent by 180° to form the loops 62. The first and second insulation parts106, 108 lie facewise adjacent to each other.

As shown in FIG. 8, the first and second insulation parts have faces116, 118 that lie adjacent to each other. It would be possible to havebare conductor locations at the ends of each loop engage each other, butmore secure holding of the conductors is achieved by surrounding eachend of the loop with insulation.

In a test clip that applicant has constructed, the flat flexible cablehas the initial and final shape shown in FIGS. 6-12. Each conductor 50has a thickness T (FIG. 9) of 0.075 mm (0.003 inch) and a width W (FIG.12) of 0.3 mm (0.012 inch). The conductors are spaced apart at a pitchor center-to-center spacing S of 0.5 mm (0.020 inch). With the thicknessT of the conductor being less than paper thin, applicant constructs theconductors of beryllium copper, to provide substantial rigidity. Exposedareas of the conductors at the loop 62 and at the upper end of thecable, are both gold plated.

The first and second insulation layers 100, 102 (FIG. 12A) are bothformed of films 103, 105 of 0.05 mm thick Kapton, with a bonding film107, 109 of 0.025 mm thick adhesive thereon. The stiffening layer 110(FIG. 9) is formed of 0.100 mm thick Kapton, with 0.05 mm thick adhesivethereon. As shown in FIG. 8, the lower end of each loop has an outsideradius R of about 0.2 mm (0.009 inch). The opposite sides 70, 72 of theloop above the curved lower end 119 are straight, and the loop has atotal height H of about 1.75 mm (0.07 inch).

As shown in FIG. 5, the flat flexible cable or connector device 52includes a middle 120 that is bent out of the vertical plane of thecable lower portion 122, and which extends to the upper end 112 of thecable. The upper end of the cable connects to a flexible cable connector124 which connects each cable conductor to a corresponding contactelement 38 of the header connector 40. The flexible cable connector 124has multiple terminals 130 which connect to the cable conductors and toconductive traces 132 on the circuit board that lead to the contactelements 38. The conductive traces 132 can include trace portions on thelower and upper surfaces of the test clip board 42 and plated-throughholes that connect the trace portions. The cable 52 is trapped in placebetween a base 140 which locates the test clip housing with respect tothe IC device, and a hood 142. A set screw 144 in the hood can betightened to fix a cable location in place.

The use of a flat flexible cable enables the characteristics of the testclip to be easily changed. IC devices are being constructed with everdecreasing lead pitches (spacing between lead centers), with the ICleads constructed by photoetching techniques that enable such decrease.Applicant's use of photoetched conductors in the cable, enablesapplicant to use the same advances in photoetching technology as areused for IC device leads, to follow the decrease in lead pitch. If thebody of a smaller pitch IC device has the same size body (e.g. 14 mmsquare) but it contains more leads at a smaller pitch (e.g. at 0.3 mminstead of at 0.5 mm), then applicant merely has to change the cable andcircuit board. The other parts of the test clip are formed of injectionmolded parts which entail large tooling costs. However, the flatflexible cable and circuit board do not involve such high tooling costs.

It is generally desirable for the lower end of each cable to pressagainst a lead with a force of about 40 grams (in a direction normal totheir surfaces). If the contact force is found to be slightly too large,applicant can alter the cable design by increasing the loop height H(FIG. 8) to make the loop less rigid, or can slightly decrease theradius of curvature R of the loop so the loop is deflected less.Opposite changes compensate for a contact force that is slightly toosmall. The exact dimensions of the IC device leads can vary from onemanufacturer to another, and the cable construction and/or mounting canbe adjusted to compensate for such variations.

FIG. 13 is a view of the bottom of the test clip, showing four fingers151-154 that lock the test clip to the IC device. Each finger has a lip160 designed to move under and against the bottom of an IC device tolock the clip to the device. As shown in FIG. 14, each finger such as151, 152 is part of the hood 142. Slots 162 separate the fingers fromfour hood sides 163 that locate lower portions of the cable, to alloweach finger to pivot. A locking ring 164 surrounds the fingers, with thelocking ring being movable vertically as indicated by arrows 166. Whenthe locking ring 164 is moved upwardly, the locking fingers 151-154 candeflect radially outwardly away from the axis 170 of the test clip. Whenthe locking ring moves downwardly, a cam surface 172 on the locking ringpushes against a tapered surface 174 on the fingers to push themtogether and lock them against corner portions of the bottom of the ICdevice.

FIG. 15 illustrates a portion of a test clip 180 which is similar tothat of FIGS. 1-14, except in the way that the upper end 182 of the flatflexible cable 184 is electrically connected to the header contacts 186of a header-type connector 188. The upper ends 182 of the conductors arebare, or uncovered by insulation. An elastomeric connector 198 connectsthe conductors to lower parts 190 of conductive traces on a test clipcircuit board 192. The lower trace parts 190 are connected throughplated holes 194 to upper trace parts 196 which connect to the headercontacts 186. The elastomeric connector 198 is of the prior art typewhich includes a horizontal stack of elastomeric wafers that are heldtogether, with electrically conductive wafers alternating withinsulative wafers; a conductive wafer connects a conductor upper end 182to a circuit board trace part 190. The connections can be soldered tomake them reliable. The connection arrangement of FIG. 15 is relativelysimple and compact because it does not use an intermediate flat cableconnector. However, in some cases a flat cable connector of the typeindicated in FIG. 5, can facilitate reliable connection to the circuitboard.

While terms such as "top", "bottom", "vertical", "horizontal" and thelike are used herein to aid in describing the invention, it should beunderstood that the parts can be used in any orientation with respect togravity.

Thus, the invention provides a connecting device which is especiallyuseful for a test clip, although useful in other applications as well,to provide a row of very small and closely spaced contacts that canreadily make and break engagements with leads or terminals. Theconnecting device comprises a flat flexible cable which includes a groupof elongated conductors and which also includes insulation which holdsto at least portions of the conductors. The insulation holds theconductor in a fixed relationship wherein they extend parallel to eachother and are laterally spaced. First end portions of the contactsextend in substantially parallel conductor loops that are each curvedabout an axis extending parallel to the lateral direction. The bentloops provide contacts or contact ends that avoid sharp edges. Theapparatus is useful primarily for contacts that are spaced apart by nomore than about one millimeter, where the ability to use simple flatconductors enables the contacts to be constructed at very low cost,despite the fact that simple flat conductors may not have as desirablemating characteristics as more complexly shaped conductors which can beconstructed at moderate cost only in large sizes. A test clip which mayinclude two or four of the flat flexible cables, holds the cables withthe conductor loops extending downwardly and positioned to wipe againstlargely vertical outer lead parts of the leads of an IC device.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art, and consequently, it isintended that the claims be interpreted to cover such modifications andequivalents.

I claim:
 1. A test clip which can test an integrated circuit device,wherein the circuit device has a device body with a body upper portionof predetermined size and a body bottom that can lie adjacent to a faceof a circuit board device, and the circuit device also has a pluralityof leads extending from each of a plurality of said body sides with eachlead having an outer lead part extending at least partially downwardlytoward the circuit board device, comprising:a clip housing with locatingwalls that closely engage said circuit device body to locate saidhousing with respect to said device body, said locating walls includinga substantially vertically extending wall; a flat flexible cable mountedon said clip housing, said cable having insulation and a plurality ofparallel elongated conductors fixed in position on said insulation, saidconductors having lower end portions with surfaces that are exposed toenable them to directly engage said leads; said cable has a lower endportion that extends in a loop wherein said loop has largely parallelopposite loop sides, with each of said conductors being exposed at saidfirst loop side, and with said conductors at said first loop side beingpositioned to engage a corresponding lead, and with both of said loopsides being at least partially deflectable to deflect away from acorresponding lead, and with at least one of said loop sides extendingupwardly and being part of a straight cable portion that presses againstsaid substantially vertically extending wall of said clip housing. 2.The test clip described in claim 1 wherein:said conductors are devoid ofsaid insulation in which said conductors are fixed in position, on bothsides of each conductor along both of said opposite loop sides.
 3. Thetest clip described in claim 1 wherein:said cable has portions that eachinclude part of a conductor, lying above each of said loop sides, whichlie facewise substantially against each other.
 4. The test clipdescribed in claim 1 wherein:said first loop side is closer to saidstraight cable portion that presses against said clip housing than issaid second loop side, along the length of said conductors.
 5. A testclip which can test an integrated circuit device, wherein the circuitdevice has a device body with a body upper portion of predetermined sizeand a body bottom that can lie adjacent to a face of a circuit boarddevice, and the circuit device also has a plurality of leads extendingfrom each of a plurality of said body sides with each lead having anouter lead part extending at least partially downwardly toward thecircuit board device, wherein the test clip includes a clip housing withlocating walls that engage said circuit device body to locate saidhousing with respect to said device body, characterized by:a flatflexible cable having a portion fixed in position on said clip housing,said cable having an insulative material and a plurality of parallelelongated conductors fixed in position on said insulative material, saidconductors having lower end portions with surfaces that are exposed toenable them to directly engage said leads; each of said conductor lowerend portions extends in a loop of at least about 180°, with each loophaving first and second sides, with said first side of each loop beingpositioned to engage a corresponding lead, with said loops being free ofrigid connection to said clip housing and with both sides of each loopbeing deflectable away from a corresponding lead, and with an extensionof at least said first side of each loop which extends away from saidsecond side, being mounted in a fixed position on said clip housing. 6.The text clip described in claim 5 wherein:both said first and secondsides of each loop have upward extensions that are each mounted in afixed position on said housing.
 7. A test clip which can test anintegrated circuit device, wherein the circuit device has a device bodywith a body upper portion of predetermined size and a body bottom thatcan lie adjacent to a face of a circuit board device, and the circuitdevice also has a plurality of leads extending from each of a pluralityof said body sides with each lead having an outer lead part extending atleast partially downwardly toward the circuit board device, wherein thetest clip includes a clip housing with locating walls that engage saidcircuit device body to locate said housing with respect to said devicebody, characterized by:a flat flexible cable having a portion fixed inposition on said clip housing, said cable having an insulative materialand a plurality of parallel elongated conductors fixed in position onsaid insulative material, said conductors having lower end portions withsurfaces that are exposed to enable them to directly engage said leads;each of said conductor lower end portions extends in a loop of at leastabout 180°, with a loop middle (74) and opposite loop sides lying onopposite sides of said loop middle, with a first of said sides of eachloop having a contact point that is positioned to engage a correspondinglead with each loop being free of rigid connection to said clip housingand with both sides of each loop being deflectable away from acorresponding lead, and with each loop being free at a height below saidcontact point, of backing material that resists deflection of either ofsaid loop side away from a corresponding lead.